1. Field of the Invention
This invention relates, broadly speaking, to the field of absorbent consumer paper products, such as towels, wipes and toilet tissue. More specifically, this invention relates to an improved drying fabric for making absorbent paper products, to the system and method of making such products, and to the product itself. This fabric design also lends itself to forming and transfer fabric applications, which may be used for making absorbent or flat grade papers.
2. Description of the Prior Art
In all paper machines, paper stock is fed onto a traveling endless belt that is supported and driven by rolls associated with the machine and which serves as the papermaking surface of the machine. In one common type of paper machine, two types of belts are used: one or more "forming" fabrics that receive the wet paper stock from the headbox or headboxes, and a "dryer" fabric that receives the web from the forming fabric and moves the web through one or more drying stations, which may be through dryers, can dryers, capillary dewatering dryers or the like. Forming, transfer, or drying belts can be formed from a length of woven fabric with its ends joined together in a seam to provide an endless belt. Fabrics can be woven endless depending on the running length of the fabric. Fabrics for this purpose generally include a plurality of spaced longitudinal warp filaments that are oriented in a machine direction ("MD") of the paper machine, and a plurality of shute (also called "weft" or "woof") filaments, oriented in a cross direction ("CD") that is orthogonal to the MD direction. The warp and shute filaments are woven together in a predetermined weave pattern that results in a distinctive pattern of "knuckles" or raised crossover locations on the fabric where a warp filament crosses over a shute filament, or vice versa. Such knuckles, when on the side of the fabric that contacts the paper web, whether it be a forming fabric, transfer, or a drying fabric, impart a depression or compressed area onto the paper web. The pattern of those depressions have a great deal to do with the texture of the finished product, irrespective of whether additional processing steps such as creping or calendaring are performed on the web.
A great deal of study has gone into developing complex fabrics for paper machines in order to provide product that is textured in a way that will be well received by consumers. For example, U.S. Pat. Nos. 3,905,863 and 3,974,025 to Ayers disclose a paper sheet and process for making it in which the back side of a semi-twill fabric is imprinted on the sheet. The sheet has a diamond-shaped pattern imprinted on it and after creping, lofted areas align in the cross direction of the sheet. Only three-shed (meaning that the crossover pattern of each warp filament will repeat every three shute crossovers) fabrics are used, which have both machine direction warp and cross direction shute knuckles in the top surface plane on the sheet side of the fabric.
U.S. Pat. No. 3,301,746 to Sanford discloses a process using imprinted fabrics that may be of a square or diagonal weave, as well as twilled or semi-twilled fabrics. The fabrics are coplanar. The product is characterized by alternately spaced, unbroken ridges of uncompressed fibers and troughs of compressed fibers, which extend in the cross machine direction. U.S. Pat. No. 4,157,276 to Wandel et al. discloses a wet end papermaking fabric of at least a five-shed, and preferably a broken twill, in an "Atlas" binding with the shute counts at least 80% of the warp counts. The warp and shute knuckles are also coplanar in the top surface plane on the sheet side. The atlas binding generally has the warp going under 1 shute and over (n-1) shutes in an n shed repeat on the sheet side.
U.S. Pat. No. 4,161,195 to Khan refers to a paper forming fabric and to the weaves themselves, which are 5-shed or greater and are woven in a non-regular twill pattern such that threads in both the MD and CD have interlacings in each weave repeat so as to be to be "evensided" and such that no MD or CD knuckle exceeds more than three crossovers in length. Generally the MD and CD knuckles on the sheet side of the fabric are coplanar in the top surface plane, although this is not a requirement. The patent refers to the above designs as "Granite" patterns. The fabric has relatively short MD knuckles, no more than 3 crossovers, even-sided fabrics, and little overlap of MD knuckles.
Trokhan, U.S. Pat. No. 4,191,609, refers to a soft imprinted paper sheet that is characterized by a patterned array of relatively closely spaced uncompressed pillow-like zones each circumscribed by a picket-like lineament comprising alternatively spaced areas of compacted and non-compacted fibers. The pillow like zones are staggered to both the MD and CD directions. The picket-like lineaments are produced by the MD and CD knuckles in the top-surface plane on the sheet side of the imprinting fabric. Trokan U.S. Pat. No. 4,239,065 refers to related paper making clothing.
Trokhan U.S. Pat. Nos. 4,528,239, 4,529,480 and 4,637,859 refer to a soft, absorbent paper web, the process for making the webs, and the foraminous fabric (or deflection member) used as an imprint/drying fabric in the process. The paper web is characterized by a relatively dense monoplanar, patterned, continuous network of compressed fibers and a plurality of relatively low density domes composed of uncompressed fibers. Each low density dome is completely encompassed and isolated by the network of compressed fibers; the domes are also staggered with respect to both the MD and CD directions. The fabric--or foraminous deflection member--is composed of a woven base on its wear side and a monoplanar, continuous network surface formed by a photosensitive resin on its sheet side.
The fabrics discussed above and the products made therefrom have proven relatively successful. However, the industry continues to strive for fabrics, processes and products that are superior in such ways as manufacturing efficiency, speed, and reliability, and in terms of product bulk, strength, texture and handfeel. This invention provides a significant advance in all of those areas.